This invention relates to isolation of low molecular weight chlorinated and chlorosulfonated resin compositions.
Chlorinated and chlorosulfonated polyolefin resins are well-known and widely available compositions which find use as general purpose elastomers as well as in adhesive, ink, and coating formulations. Such compositions are highly resistant to attack by acids, bases, and solvents, and, in addition, they display a high degree of moisture resistance, flexibility, ozone resistance, and excellent adhesion to a wide variety of substrates. The resins are compatible with most components of adhesive and coating formulations and consequently it is possible to impart the chemical resistance, wet adhesion, and elastomeric properties of the resins themselves to these formulations by blending. In addition, particularly in the case of the chlorosulfonated resins, chemical reaction of the chlorinated resin with one or more of the components of the formulation can impart even greater improvements in chemical, physical, and mechanical properties.
The resins are prepared on an industrial scale by chlorination or chlorosulfonation of polyolefins in solution or in aqueous or non-aqueous suspension. Solution processes are preferred because the products obtained have a greater degree of homogeneity than those produced in suspension. The solvents which are used as reaction media for solution polymerization are preferably substantially inert to chlorination and easily removed from the chlorinated polymer product. Isolation is generally effected by use of drum dryers whereby a pair of heated drum rolls situated closely adjacent to one another are fed with a solution of polymeric material which collects in a nip pool above the nip of the rolls. As the solvent evaporates a film of polymeric material is deposited on the drum surface as it contacts the nip pool. The film is usually removed from the rolls by means of a doctor knife and the polymeric product formed is gathered into a rope which is cut into chips for packaging. Alternatively, the polymer solution can be fed to a devolatilizing extruder in which the solvent is removed by means of heat and vacuum, and the resulting polymer extrudate can be recovered in film, powder, or pellet form, or as a strand.
Although these isolation procedures work well for recovery of most chlorinated or chlorosulfonated polymers, these techniques are not suitable for polymers of low molecular weight. Such resins do not have sufficient melt strength to form a film on the drum of a drum dryer. In addition, the film strength of such compositions is insufficient to permit easy release from the drum and in many cases the film tend to gather on the doctor blade resulting in overheating and degradation of the polymer. Further, it is difficult to gather low molecular weight resins into a flexible rope which can be conveyed to a cutter without rupture. Isolation by means of a devolatilizing extruder is also impractical for the low molecular weight chlorinated polymers because these material cannot be formed into a strand, a film, or into pellets due to inadequate film strength. The extrudate cannot be conveyed and must be collected in a container, often resulting in overheating and degradation of the polymer. Thus, it has been necessary to employ other less economical processes for isolation of low molecular weight chlorinated resins, for example precipitation via a non-solvent followed by distillation to remove the solvent and non-solvent, and subsequent drying of the product.
The present invention provides a method for isolation of low molecular weight chlorinated or chlorosulfonated resins wherein the melt strength of the chlorinated olefin polymers is increased without adversely affecting the chemical and physical properties or the solution characteristics of the chlorinated or chlorosulfonated resin products.